How do I install the Bitcoin Segwit skill?

Run npx skillmds@latest add claude-dev-suite/bitcoin-segwit in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Bitcoin Segwit safe to use?

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Which AI agents work with Bitcoin Segwit?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Bitcoin Segwit free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Bitcoin Segwit?

claude-dev-suite (@claude-dev-suite) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Bitcoin Segwit by claude-dev-suite — Agent Skill

Name: Bitcoin Segwit
Rating: 4.2 (5 reviews)
Author: claude-dev-suite

Bitcoin Segwit

Segregated Witness: BIP141 (consensus), BIP143 (sighash), BIP144 (P2P serialization), BIP173 (Bech32 address). Witness segregation, weight units, txid vs wtxid, witness commitment. USE WHEN: working with native segwit (P2WPKH/P2WSH), embedded segwit (P2SH-P2WPKH/P2SH-P2WSH), or understanding the witness discount.

claude-dev-suite Updated Sep 8, 2026 28 repo stars

File contents

SegWit (BIP141 family)

Activated August 2017. Moved signatures and other auxiliary data into a new witness section that is not included in txid hashing.

Goals achieved

Fixed transaction malleability for SegWit-only inputs.
Weight discount — witness bytes count 1 WU (vs 4 WU for base). Effective block size cap rose from 1 MB to ~4 MWU.
Linear sighash (BIP143) — O(n) signing instead of O(n²) for multi-input txs.
Soft-fork upgrade path — version field on witness program enables future versions (1 = Taproot).

Witness program structure

scriptPubKey for SegWit outputs:

<version_byte> <data_push>

Version byte = OP_0 (v0), OP_1 (v1 = Taproot, BIP341). Future versions reserved.

Length of data push determines type:

v0, 20 bytes: P2WPKH
v0, 32 bytes: P2WSH
v1, 32 bytes: P2TR
Other v0 lengths: invalid (consensus failure post-activation).
v2..v16 with any length: forward-compat (anyone-can-spend until future soft fork).

Address encoding (BIP173 / BIP350)

Bech32 (BIP173) for v0 → bc1q... (mainnet), tb1q... (testnet).
Bech32m (BIP350) for v1+ → bc1p.... Different checksum constant to fix BIP173 length-extension bug.

Encoding helpers usually check the witness version byte and auto-select Bech32 vs Bech32m.

Embedded SegWit (legacy compat)

For wallets that can only produce P2SH addresses:

P2SH-P2WPKH:
- scriptPubKey = OP_HASH160 <H160(redeemScript)> OP_EQUAL
- redeemScript = OP_0 <H160(pk)>
- scriptSig = OP_PUSH(redeemScript)
- witness = [<sig>, <pk>]
P2SH-P2WSH: similar with 32-byte witness program.

Sighash (BIP143)

For SegWit v0 inputs, sighash is computed over a precomputed digest: hashPrevouts || hashSequence || outpoint || scriptCode || amount || nSequence || hashOutputs || nLockTime || nHashType.

Two key facts:

The input amount is committed → fee-bumping attack with old signatures is detected (each input value is signed).
hashPrevouts, hashSequence, hashOutputs are reused across all inputs → O(n) total cost.

Taproot (BIP341) supersedes this with an even cleaner digest.

P2P relay (BIP144)

Old nodes see SegWit transactions as anyone-can-spend (witness stripped).
New nodes use service flag NODE_WITNESS (1 << 3) to advertise witness support.
Block download: getdata with type MSG_WITNESS_BLOCK for full witness data.

Common gotchas

Forgetting marker/flag (0x00, 0x01) bytes when serializing for network → wire-format invalid.
Computing txid over the segwit serialization (with witness) → wrong, must strip witness for txid.
Using P2SH-P2WPKH addresses (3...) when wallet supports native P2WPKH (bc1q...) → wastes ~10 vB per input.
Mixing v1 (Taproot) outputs and assuming Bech32 addresses → must use Bech32m, otherwise checksum is rejected by spec-compliant wallets.

---name: bitcoin-segwitdescription: Segregated Witness: BIP141 (consensus), BIP143 (sighash), BIP144 (P2P serialization), BIP173 (Bech32 address). Witness segregation, weight units, txid vs wtxid, witness commitment. USE WHEN: working with native segwit (P2WPKH/P2WSH), embedded segwit (P2SH-P2WPKH/P2SH-P2WSH), or understanding the witness discount.---# SegWit (BIP141 family)Activated August 2017. Moved signatures and other auxiliary data intoa new **witness** section that is **not** included in `txid` hashing.## Goals achieved1. **Fixed transaction malleability** for SegWit-only inputs.2. **Weight discount** — witness bytes count 1 WU (vs 4 WU for base). Effective block size cap rose from 1 MB to ~4 MWU.3. **Linear sighash** (BIP143) — O(n) signing instead of O(n²) for multi-input txs.4. **Soft-fork upgrade path** — version field on witness program enables future versions (1 = Taproot).## Witness program structure`scriptPubKey` for SegWit outputs:```<version_byte> <data_push>```Version byte = `OP_0` (v0), `OP_1` (v1 = Taproot, BIP341). Futureversions reserved.Length of data push determines type:- v0, 20 bytes: P2WPKH- v0, 32 bytes: P2WSH- v1, 32 bytes: P2TR- Other v0 lengths: invalid (consensus failure post-activation).- v2..v16 with **any** length: forward-compat (anyone-can-spend until future soft fork).## Address encoding (BIP173 / BIP350)- Bech32 (BIP173) for v0 → `bc1q...` (mainnet), `tb1q...` (testnet).- **Bech32m** (BIP350) for v1+ → `bc1p...`. Different checksum constant to fix BIP173 length-extension bug.Encoding helpers usually check the witness version byte andauto-select Bech32 vs Bech32m.## Embedded SegWit (legacy compat)For wallets that can only produce P2SH addresses:- **P2SH-P2WPKH**: - `scriptPubKey = OP_HASH160 <H160(redeemScript)> OP_EQUAL` - `redeemScript = OP_0 <H160(pk)>` - `scriptSig = OP_PUSH(redeemScript)` - `witness = [<sig>, <pk>]`- **P2SH-P2WSH**: similar with 32-byte witness program.## Sighash (BIP143)For SegWit v0 inputs, sighash is computed over a precomputed digest:`hashPrevouts || hashSequence || outpoint || scriptCode || amount ||nSequence || hashOutputs || nLockTime || nHashType`.Two key facts:1. The **input amount** is committed → fee-bumping attack with old signatures is detected (each input value is signed).2. `hashPrevouts`, `hashSequence`, `hashOutputs` are reused across all inputs → O(n) total cost.Taproot (BIP341) supersedes this with an even cleaner digest.## P2P relay (BIP144)- Old nodes see SegWit transactions as anyone-can-spend (witness stripped).- New nodes use service flag `NODE_WITNESS` (1 << 3) to advertise witness support.- Block download: `getdata` with type `MSG_WITNESS_BLOCK` for full witness data.## Common gotchas- Forgetting `marker/flag` (0x00, 0x01) bytes when serializing for network → wire-format invalid.- Computing `txid` over the segwit serialization (with witness) → wrong, must strip witness for txid.- Using P2SH-P2WPKH addresses (`3...`) when wallet supports native P2WPKH (`bc1q...`) → wastes ~10 vB per input.- Mixing v1 (Taproot) outputs and assuming Bech32 addresses → must use Bech32m, otherwise checksum is rejected by spec-compliant wallets.## See also- [transactions/SKILL.md](../transactions/SKILL.md)- [taproot/SKILL.md](../taproot/SKILL.md)- [scripts/SKILL.md](../scripts/SKILL.md)

Frequently asked questions